On Tue, Aug 28, 2007 at 02:00:43PM -0500, Robin Holt wrote:

The ioctl is sort of historical.  IIRC, in ProPack 3 (RHEL4 based 2.4
kernel), we added system calls.  When the community started making noise
about system calls being bad, we went to a device special file with a
read/write (couldn't get the needed performance from the ioctl() interface
which used to acquire the BKL).  Now that the community fixed the ioctl
issues, we went to using an ioctl, but are completely open to change.

If you want to introduce system calls, we would expect to need, IIRC, 8.
We also pondered an xpmem filesystem today.  It really felt wrong,
but we could pursue that as an alternative.

The problem is not ioctls per sae, but the kind of operation you
export.

What is the correct direction to go with this?  get_user_pages() does
currently require the task_struct.  Are you proposing we develop a way
to fault pages without the task_struct of the owning process/thread group?

Stop trying to mess with vmas and get_user_pages on processes entirely.
The only region of virtual memory a driver can deal with is the one it
got a mmap request for, or when using get_user_pages the one it's got
a read/write request for.  You're doing a worse variant of the rdma page
pinning scheme we're rejected countless times.

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